1. Field of Invention
The present invention relates to a torque-controlling wrench and, more particularly, to a torque-controlling wrench with a spring that is compressed evenly, thus elongating the life thereof.
2. Related Prior Art
A torque-controlling wrench is used to protectively exert a controllable torque on a fastener such as a threaded bolt and a nut. When the torque exerted on the fastener reaches a pre-determined value, the driving of the fastener by the torque-controlling wrench is interrupted for avoiding excessive engagement of the thread of the threaded bolt with the thread of the nut, damage of the threads of the threaded bolt and nut and/or damage of the head of the threaded bolt or the nut. Hence, the threaded bolt can be disengaged from the nut.
Referring to FIGS. 1 through 4, there is shown a conventional torque-controlling wrench. The conventional torque-controlling wrench includes a handle 10 that is hollow, a socket-driving unit 15 installed at an end of the handle 10 and a torque-controlling device 20 installed in the handle 10 and connected to the socket-driving unit 15. The torque-controlling device 20 includes a rod 21 connected to the socket-driving unit 15, a knob 23 and a spring 22 compressed between the rod 21 and the knob 23 that can be turned to adjust the force exerted on the rod 21 by the spring 22. For the stability and precision of the contact of the rod 21 with the spring 22, there is generally an intermediate mechanism 24. The intermediate mechanism 24 includes a roller 25 installed at an end of the rod 21 and a rolling gear installed at an end of the spring 22. The rolling gear includes a frame 26 installed in the handle 10, a shaft 27 installed on the frame 26, a wheel 28 installed on the shaft 27 and a roller 29 installed on the frame 26. The center of the roller 25 is located on a side of a vertical line passing the center of the shaft 27 while the center of the roller 29 is located on the other side of the vertical line. As shown in FIG. 4, when torque exerted on a fastener by the torque-controlling wrench reaches a pre-determined value, the rod 21 will be moved downwards. The movement of the rod 21 is not supposed to cause the pivoting of the frame 26 due to the use of the roller 25 and the wheel 28 both of which are expected to roll smoothly. However, the roller 25 and the wheel 28 generally do not roll as smoothly as expected. The movement of the rod 21 causes the pivoting of the frame 26 in practice. When the frame 26 is pivoted, the spring 22 will be bent instead of compressed. Hence, the driving of the fastener by the torque-controlling wrench will not be interrupted as expected.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.